During the after-treatment of exhaust gases of an internal combustion engine, the exhaust gas sensors that are arranged according to respective exhaust gas elements, such as filters and catalytic converters for after-treatment, are very important for a pollutant-optimized operation of the internal combustion engine.
Exhaust gas sensors are generally employed to monitor exhaust gas values before and after respective exhaust gas after-treatment elements and to ensure that legal requirements, which are defined for example by limiting value for exhaust gas values, are complied with. Accordingly, exhaust gas sensors are often prescribed by legal statutes for controlling the operation of an internal combustion engine.
In order to make it possible to ensure a correct functioning of respective exhaust gas sensors, the sensors are calibrated during the operation of an internal combustion engine based on specifically defined exhaust gas concentrations. For this purpose, the function of the exhaust gas sensor must be according to legal statutes verifiable during the operation of the internal combustion engine.
In order to test the function of an exhaust gas sensor, an exhaust gas system is impacted with a defined exhaust gas amount and concentration of pollutants. The exhaust gas values obtained during the impacting of the exhaust gas sensor, such as for example concentrations of pollutants, are then compared to a predetermined target value in order to infer therefrom malfunctions and/or deviations in the measurement behavior of the exhaust gas sensor. So as to examine the exhaust gas sensors and the elements of the after-treatment of the gas sensors arranged in a exhaust gas system, it is necessary to temporarily suppress the elements for post treatment of the exhaust gas and to impact the exhaust gas sensors with untreated exhaust gas.
As statutory requirements become more and more strict, it can sometime occur that the concentration in a stream of exhaust gas which is used with exhaust gas sensors arranged behind the respective elements for post treatment of exhaust gas exceeds the legally prescribed limiting value for a concentration of pollutants, so that a corresponding exhaust gas system generates during the examination of respective exhaust gas sensors of the exhaust gas system a value that exceeds the legally prescribed limiting value. Accordingly, there is a need for a method for diagnosing an exhaust gas sensor arranged behind respective exhaust gas post treatment elements of an exhaust gas system while remaining in compliance with applicable regulations for exhaust gas.
The European patent document EP 2 960 453 A1 discloses an exhaust gas system that is provided with a main line and with a secondary line.
In the European patent document EP 0 525 566 A1 is described an exhaust gas system that is provided with a plurality of filters.
The German patent document DE 2006 010 497 A1 discloses a exhaust gas system provided with an exhaust gas path, which is equipped with a first filter and with a second filter arranged in the direction of the flow downstream of the first filter.